Tablets that disintegrate or dissolve rapidly in the patient's mouth without the use of water are convenient for the elderly, young children, patients with swallowing difficulties, and in situations where water is not available. For these specially designed formulations, the small volume of saliva that is available is sufficient to disintegrate or dissolve a tablet in the oral cavity. The drug released from these tablets can be absorbed partially or entirely into the systemic circulation from the buccal mucosa or sublingual cavity, or can be swallowed as a solution to be absorbed from the gastrointestinal tract.
The sublingual route usually produces a faster onset of action than traditional orally-administered tablets and the portion absorbed through the sublingual blood vessels bypasses the hepatic first pass metabolic processes (Birudaraj et al., 2004, J Pharm Sci 94; Motwani et al., 1991, Clin Pharmacokinet 21: 83-94; Ishikawa et al., 2001, Chem Pharm Bull 49: 230-232; Price et al., 1997, Obstet Gynecol 89: 340-345; Kroboth et al., 1995, J Clin Psychopharmacol 15: 259-262; Cunningham et al., 1994, J Clin Anesth 6: 430-433; Scavone et al., 1992, Eur J Clin Pharmacol 42: 439-443; Spenard et al., 1988, Biopharm Drug Dispos 9: 457-464).
Likewise, due to high buccal and sublingual vascularity, buccally- or sublingually-delivered drugs can gain direct access to the systemic circulation and are not subject to first-pass hepatic metabolism. In addition, therapeutic agents administered via the buccal or sublingual route are not exposed to the acidic environment of the gastrointestinal tract (Mitra et al., 2002, Encyclopedia of Pharm. Tech., 2081-2095). Further, the buccal and sublingual mucosas have low enzymatic activity relative to the nasal and rectal routes. Thus, the potential for drug inactivation due to biochemical degradation is less rapid and extensive than other administration routes (de Varies et al., 1991, Crit. Rev. Ther. Drug Carr. Syst. 8: 271-303).
The buccal and sublingual mucosas are also highly accessible, which allows for the use of tablets which are painless, easily administered, easily removed, and easily targeted. Because the oral cavity consists of a pair of buccal mucosa, tablets, such as fast disintegrating tablets, can be applied at various sites either on the same mucosa or, alternatively, on the left or right buccal mucosa (Mitra et al., 2002, Encyclopedia of Pharm. Tech., 2081-2095). In addition, the buccal and sublingual routes could be useful for drug administration to unconscious patients, patients undergoing an anaphylactic attack, or patients who sense the onset of an anaphylactic attack.
Anaphylaxis is a sudden, severe systemic allergic reaction, which can be fatal within minutes. Epinephrine (Epi) is the drug of choice for the treatment of anaphylaxis worldwide (Joint Task Force on Practice Parameters, 2005, J Allergy Clin Immunol 115: S483-S523; Lieberman, 2003, Curr Opin Allergy Clin Immunol 3: 313-318; Simons, 2004, J Allergy Clin Immunol 113: 837-844). It is available as an injectable dosage form in ampoules or in autoinjectors, however these are underused when anaphylaxis occurs (Simons, F. E. R. J Allergy Clin Immunol 124(4):625-636 2009; Simons, F. E. R. J Allergy Clin Immunol 125:S161-181 2010). The drawbacks of Epi auto-injectors include high cost, perceived large size and bulkiness, limitations on repeated dosing (if required), fear and anxiety associated with the use of needles (especially in children), and dosing errors caused by incorrect techniques of administration (Simons, K. J. et al. Current Opinion in Clinical Immunology 10:354-361 2010). Furthermore, in aqueous solutions, epinephrine is unstable in the presence of light, oxygen, heat, and neutral or alkaline pH values (Connors et al., 1986, in Chemical Stability of Pharmaceuticals: A Handbook for Pharmacists, Wiley-Interscience Publication: New York) and thus has limited shelf-life; approximately one year.
The sublingual route of administration is a promising alternative route for epinephrine administration. The formulation of sublingual tablets of epinephrine would enable the development of tablets with a range of epinephrine doses to match the population on an mg/kg basis. Sublingual tablets of epinephrine would be easy to carry and self-administer eliminating the fear and anxiety associated with needles used in autoinjectors for young children, as well as readily providing the capability of multiple doses. Feasibility studies in humans and animals have shown that epinephrine can be absorbed sublingually (Gu et al., 2002, Biopharm Drug Dispos 23: 213-216; Simons et al., 2004, J Allergy Clin Immunol 113: 425-438). The recommended dose of epinephrine for the treatment of anaphylaxis is about 0.01 mg/Kg: usually about 0.2 mL to about 0.5 mL of a 1:1000 dilution of epinephrine in a suitable carrier. Based on historical and anecdotal evidence, an approximately 0.3 mg dose of epinephrine, by subcutaneous (SC) or intramuscular (IM) injection into the deltoid muscle, has been agreed upon as the dose required for the emergency treatment of anaphylaxis. Recent studies have demonstrated that if the approximately 0.3 mg dose is administered IM into the laterus vascularis (thigh) muscle, Epi plasma concentrations are higher and occur more quickly than SC or IM administration into the deltoid muscle. (Joint Task Force on Practice Parameters, 2005, J Allergy Clin Immunol 115: S483-S523; Lieberman, 2003, Curr Opin Allergy Clin Immunol 3: 313-318; Simons, 2004, J Allergy Clin Immunol 113: 837-844)).
As stated above, epinephrine (Epi) is typically administered either subcutaneously (SC) or intramuscularly (IM) by injection. Thus, Epi injections are the accepted first aid means of delivering Epi and are administered either manually or by automatic injectors. It is recommended that persons at risk of anaphylaxis, and persons responsible for children at risk for anaphylaxis, maintain one or more automatic Epi injectors in a convenient place at all times.
Given the difficulties associated with manual subcutaneous (SC) or intramuscular (IM) administration of Epi, such as patient apprehension related to injections or the burden of an at risk person having to always maintain an Epi injector close at hand, there exists a need in the art for more convenient dosage forms which can provide immediate administration of Epi, particularly to a person undergoing anaphylaxis wherein the need for injection or Epi injectors is obviated.
Recently, a novel fast-disintegrating tablet suitable for sublingual (SL) administration of Epi was developed. See related U.S. applications: U.S. Provisional Patent Application No. 60/715,180; U.S. Provisional Patent Application No. 60/759,039; U.S. Utility patent application Ser. No. 11/672,503; and U.S. Utility patent application Ser. No. 11/530,360. Sublingual administration of 40 mg epinephrine as the bitartrate salt using these novel tablets resulted in a rate and an extent of epinephrine absorption similar to that achieved following intramuscular injections of 0.3 mg epinephrine in the thigh. Sublingual doses ranging from 5 to 40 mg epinephrine as the bitartrate salt were studied to achieve equivalent plasma concentrations. In an animal model, it was determined that a 40 mg epinephrine dose administered sublingually as a bitartrate salt in tablet form resulted in plasma epinephrine concentrations similar to those achieved by 0.3 mg epinephrine intramuscular (IM) injection (Rawas-Qalaji et al. J Allergy Clin Immunol 117:398-403 2006).
Without being bound by theory, it is thought that fabrication of epinephrine into fine particles, including epinephrine nanoparticles or nanocrystals and epinephrine microparticles or microcrystals, and incorporation of the epinephrine fine particles into a tablet formulation with pharmaceutically-acceptable carriers, penetration enhancers, and mucoadhesives will significantly increase the absorption of SL-administered epinephrine and will result in the reduction of SL epinephrine dose required.